Ophthalmologic surgery typically requires the use of a physiologic irrigation solution to protect and maintain the physiological integrity of intraocular tissues. Examples of ophthalmologic surgical procedures usually requiring irrigation solutions are cataract operations, corneal transplant operations, vitreoretinal operations and trabeculectomy operations for glaucoma.
Solutions that have been used in ophthalmologic surgical irrigation include normal saline, lactated Ringer's solution and Hartmann's lactated Ringer's solution, but these are not optimal due to potential unfavorable corneal and endothelial effects. Other aqueous solutions that include agents such as electrolytes, buffering agents for pH adjustment, glutathione and/or energy sources such as dextrose, better protect the tissues of the eye, but do not address other physiologic processes associated with surgery. One commonly used solution for ophthalmologic irrigation is a two part buffered electrolyte and glutathione solution disclosed in U.S. Pat. No. 4,550,022 to Garabedian et al., the disclosure of which is hereby expressly incorporated by reference. The two parts of this solution are mixed just prior to administration to ensure stability. These solutions are formulated with a goal of maintaining the health of ocular tissues during surgery.
Modifications of conventional aqueous irrigation solutions by the addition of therapeutic agents have been proposed. For example, U.S. Pat. No. 5,523,316 to Gan et al. discloses the addition of one or more agents for controlling intraocular pressure to irrigation solutions. Specific examples of agents for controlling intraocular pressure disclosed in the Gan et al patent, all disclosure of which is hereby incorporated by reference, are beta-blockers (i.e., beta adrenergic receptor antagonists) and alpha-2 adrenergic receptor agonists. Reference is also made to muscarinic agonists, carbonic anhydrase inhibitors, angiostatic steroids and prostaglandins as classes of drugs that control intraocular pressure. Only agents intended for the control of intraocular pressure are envisioned.
Another example of a modified solution is disclosed in International PCT Application WO 94/08602 in the name of inventors Gan et al., the disclosure of which is hereby incorporated by reference. This application discloses the inclusion of a mydriatic agent, such as epinephrine, in ocular irrigation solutions. Still another example is provided by International PCT Application WO 95/16435 in the name of inventors Cagle et al., which discloses the inclusion of non-steroidal anti-inflammatory drugs (NSAIDs) in an ophthalmologic irrigation solution.
A topical ophthalmologic solution is disclosed in U.S. Pat. No. 5,811,446 to Thomas that includes histidine, and which may include at least one other active agent such as an anti-glaucoma agent, such as timolol or phenylephrine, a steroid or an NSAID. This reference teaches application of the composition to limit the inflammation associated with ophthalmic procedures. The solution is administered by a dropper into the cul-de-sac of the eye.
U.S. Pat. No. 5,624,893 to Yanni includes compositions including a wound healing agent, such as a steroid or a growth factor, and/or a pain mediator, such as an NSAID, a bradykinin antagonist, or a neurokinin-1 antagonist. The compositions are intended for the treatment and prevention of corneal haze associated with laser irradiation and photoablation.
Although many topically applied agents are available or have been proposed to treat ocular inflammation, produce mydriasis (typically necessary to perform many types of ophthalmologic surgery), or to control intraocular pressure, no previous attempt has been made to combine these agents for use in a perioperative ocular irrigation solution that is delivered in such a way so as to provide a constant, controlled delivery of multiple therapeutic agents, that act on multiple molecular targets to address multiple physiologic functions, to the tissues of the eye throughout a procedure.
Various methods of ocular drug delivery are conventionally employed, each of which has limitations. These limitations may include corneal and conjunctival toxicity, tissue injury, globe perforation, optic nerve trauma, central retinal artery and/or vein occlusion, direct retinal drug toxicity, and systemic side effects. For example, topical medications applied drop-wise are frequently impeded in reaching a targeted ocular site due to the eye's natural protective surface. In many situations, a rather small percentage of the medication applied to the surface of the eye will actually reach the desired therapeutic site of action.
One difficulty in ocular drug delivery during surgical procedures is to achieve the desired therapeutic concentration levels with the proper temporal control. The most desired pharmacokinetic effect is to be able to rapidly achieve a therapeutic concentration range and subsequently maintain the drug concentration at a constant level. This is not achieved by conventional methods of ocular drug delivery. The challenge of achieving similar pharmacokinetic profiles is substantially compounded when it is desirable to simultaneously deliver more than one drug. A unique group of factors affect the ability of a drug to penetrate the corneal epithelia, including the size of the molecule, its chemical structure and its solubility characteristics.
To achieve sufficient concentration of drug delivered to the back of the eye, drugs are frequently administered systemically at very high doses. These levels are necessary to overcome the blood-retina barrier that protects the back of the eye from selected drug molecules coming from the blood stream. For surgical procedures, injectable drug solutions are sometimes injected directly into the back of the eye. Subconjuctival and peribulbar periocular injections are used when higher local concentrations are needed and when drugs with poor penetration characteristics need to be delivered. Intracameral injections directly into the anterior chamber are used in cataract surgery. While intracameral injection provides a prompt method of achieving a concentration, it can be associated with corneal toxicity. However, this method suffers from the fact that these drugs are quickly removed by the eye's natural circulatory process. Thus, injectable solutions rapidly lose their therapeutic benefit, often necessitating frequent, large dose injections that can carry toxicity risks. Sustained release formulations, such as viscoelastic gels containing microcapsules, may be injected intraocularly for a longer duration of action. However, there may be some delay in reaching a local therapeutic concentration of drug. Hence, there exists a need for controlled methods of ocular delivery during ophthalmologic procedures.